The indicated circuit uses an unusual buffer from National Semiconductor. The frequency is given by resistors R1 and R2 as well as capacitors C1 and C2.
This filter rejects 1 kHz signals, being suggested by the manufacturer of the operational...
This is a simple variac type source found in the July 1962 Radio Electronics magazine. Voltage and...
The current of this source is 200 mA at the most, and the output depends on the zener that may...